Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$138.68	4.320%	$144.671	$144.67	$144.65	$144.70
Purchase #2	$119.63	10.286%	$131.9351	$131.94	$131.95	$131.90
Purchase #3	$74.84	4.637%	$78.3103	$78.31	$78.30	$78.30
Purchase #4	$60.65	7.590%	$65.2533	$65.25	$65.25	$65.30
Purchase #5	$34.88	11.250%	$38.804	$38.80	$38.80	$38.80
Purchase #6	$131.62	10.340%	$145.2295	$145.23	$145.25	$145.20
Purchase #7	$157.83	13.638%	$179.3549	$179.35	$179.35	$179.40
7 purchase totals =	$718.13		$783.5581	$783.55	$783.55	$783.60